The present invention relates to slide core molds for use in injection molding, and more specifically to slide mechanisms employed in such molds.
Conventional molds for injection molding typically comprise mating parts, such as a core and a cavity, which abut each other at a parting line and are moved directly away from each other along a machine axis during opening of the mold.
Such molds may also include one or more mold components which form an undercut portion of the article to be molded. These mold components, also to herein as xe2x80x9cslide insertsxe2x80x9d, are moved laterally into and out of engagement with the other mating parts of the mold during closing and opening of the mold. Usually, a pair of such slide inserts is provided, one slide insert on each side of the mold. During mold opening, the slide inserts are moved outwardly in opposite directions from the other mating parts of the mold. Molds which include such laterally movable components are referred to herein as xe2x80x9cslide core moldsxe2x80x9d.
Presently used mechanisms for opening and closing slide core molds typically include slide blocks on which the slide inserts are mounted. Usually, these slide blocks are slidably mounted on the mold plate which carries the core, with one slide block being provided on each side of the mold. Lateral movement of the slide blocks is accomplished by providing angled horn pins mounted to the mold plate which carries the cavity. The horn pins extend through angled apertures in the slide blocks. As the core is separated from the cavity, the slide blocks slide along the horn pins, resulting in outward displacement of the slide blocks and the associated slide inserts from the other mating parts of the mold.
Examples of this type of mechanism are described in U.S. Pat. No. 3,811,645 issued May 21, 1974 to Feist and U.S. Pat. No. 4,889,480 issued Dec. 26, 1989 to Nakamura et al. These two pat. are actually concerned with slide retainers which are required in this type of slide core mold since the horn pins and the apertures in the slide blocks may become misaligned when the mold is opened, preventing reinsertion of the horn pins into the slide blocks.
Conventional slide mechanisms have several disadvantages. Firstly, conventional slide mechanisms include components such as cams which must be mounted on the outside of the mold and which increase the size of the mold. Some conventional slide retainers, such as the pull rod/compression spring retainer shown in FIG. 2 of the Feist patent, also include components which project from the sides of the mold. These components have the effect of enlarging the mold, reducing the number of mold cavities which can be fitted into a molding apparatus of a given size.
In addition, components such as cams and/or horn pins project from the parting line face and obstruct the space between the mold plates during ejection of the molded parts from the core. Since these components are lubricated, contact with the molded parts during ejection can result in product contamination.
Another disadvantage of conventional slide mechanisms is that these mechanisms are actuated as the mold opens and closes. This requires that the opening and closing of the mold be slowed down In order to avoid damaging the relatively delicate slide inserts, thereby lengthening the mold cycle time.
Therefore, the need exists for an effective slide mechanism which eliminates or reduces the size and/or number of components projecting from the outside of the mold. It would also be desirable to provide a slide mechanism which eliminates the need for a slide retainer to reduce the size and complexity of the mechanism, which also eliminates obstructions between the mold plates, and which can be actuated independently of opening and closing the mold.
The present invention overcomes at least some of the disadvantages of the prior art by providing a molding apparatus having a slide mechanism which is more compact than conventional slide mechanisms, does not form obstructions between the open mold plates, eliminates the need for slide retainers, and does not depend on mold opening and closing for actuation.
The molding apparatus according to the present invention comprises at least two mold plates which preferably carry a plurality of mold cores and mating mold cavities which form a plurality of molds. Each mold has a pair of laterally movable mold elements which are movable toward and away from each other. The mold elements of each mold are mounted on a pair of slides positioned on either side of the mold.
The mechanism for moving the mold elements between their inner and outer positions includes a reciprocating driving rack which drives at least one pinion. Each pinion drives a pair of driven racks which are movable in opposite directions, each of the racks being connected to one of the slides. Therefore, movement of the driving rack results in lateral movement of the slides and the associated mold components inwardly or outwardly in relation to the mold.
Since the apparatus of the invention does not utilize horn pins, misalignment of the slides during opening and closing is not a problem, and therefore slide retainers are not required. The slide mechanism of the present invention is compact and is recessed into the stripper plate, away from the mold parting line. This reduces the overall size of the mold and eliminates obstructions between the mold plates, thereby reducing the risk of contamination of parts being ejected from the molds. Furthermore, the slide mechanism does not rely on mold opening and closing for actuation since the driven racks are preferably actuated by a pneumatic cylinder after the mold is opened and retracted before it is closed, thereby allowing a shorter mold cycle time.